1. Field of the Invention
The present invention relates to apparatus for aligning X-Y scanner axes to register a light image with respect to a form slide on an image receiving member.
The invention is especially suitable for use in computer output microfilmers (COM) wherein successive lines of alphanumeric characters are scanned across a film to record a page of computer output data. The invention is generally applicable for use in mirror scanning apparatus wherein beams of light are reflected off nutating mirrors for providing images with a high degree of accuracy and resolution.
This type of accurate registration is referred to as "character splitting" in COM units and means that, everywhere over the film image, form slide lines will appear inbetween adjacent characters without touching them. The mechanism for achieving this accuracy and resolution is an image generator system whose optical and mechanical components are carefully toleranced and, when assembled, are aligned according to a rigorous and well planned alignment procedure. The present invention facilitates such an alignment procedure by allowing minute and independent adjustment of the scanner axis for each mirror with no mirror translation; thereby insuring perpendicular scanning.
2. Description of The Prior Art
In the computer output microfilmers, computer data can be converted into light beams which are scanned on to a a film for recording the alphanumeric characters which represent the computer data. It has beem found desirable to use a mirror which is controlled by a galvanometer for scanning the light beams to write a line of characters on the film. Successive lines may be written by advancing the film. However, in the interest of increasing writing speed and accuracy, it is desirable to use a second galvanometer rotated mirror to scan the beams in a direction perpendicular to the direction of the lines; thus permitting a complete page of computer output data to be written, said in one frame of the film.
In the course of microfilming operations, it is necessary to record on the film pages of very small size and for this reason misalignment of the mirrors cannot be tolerated. Proper alignment of the mirrors is requisite to providing parallelism of the characters with respect to one another as well as with format lines superimposed from a form slide. For example, if the displayed data has shifted vertically downward by one or two lines this may indicate that the mirror has been dislodged out of its proper plane such that the mirror top has physically moved towards the page; thus adjustment of the scanner axis will be required to properly position the characters.
In the past, different techniques have been utilized to accomplish this adjustment such as physically repositioning the mirror on the shaft of the galvanometer. However, because the adjusting mechanism itself was located on the shaft of the mirror the mass that the galvanometer had to rotate was increased significantly, resulting in over-shoot problems because of the increased inertia.
In an effort to reduce the mass that the galvanometer must rotate, an adjustable base was provided in which the galvanometer was mounted. Thus, by adjusting the mount which supports the galvanometer the mirror could be repositioned.
Some of these earlier mounts utilized shim arrangements to adjust the position of the scanner axis. However, when this type of mount was used, it was found that the center of the mirror was displaced, as a result of the adjustment, which introduced undesirable distortion.
Another type of mount that was utilized was a ball and socket arrangement. The galvanometer was mounted on a shelf which terminated in a spherical portion which engaged a complementary concave base unit. Nylon tipped screws were provided in the spherical portion to slidably adjust the position of the spherical surface in the socket which in turn adjusted the axis of the scanner.
It was found that this type of mount allowed the center of the mirror to remain fixed when the scanner axis was adjusted. However, it was also found to complicate the alignment procedure since it did not allow independent adjustment of the axes. Any adjustment in the mirror plane affected the alighment in the mirror normal plane and visa versa.